Beijing environmental protection departments strengthened regulations on heavy-duty diesel vehicle emissions in 2017 in the capital city's battle to cut down air pollutants and improve air quality.

In 2017, the city inspected 20.04 million vehicles on roads, of which 58,000 heavy-duty diesel vehicles failed the tests.

Heavy-duty diesel vehicles have long been regarded as one of the key sources of vehicle emissions by environmental protection departments and their inspections have become a vital part in their routine work.

Although the number of heavy-duty diesel vehicles accounts for only 4 percent of vehicles in the city, their emissions of nitrogen oxide and particulates account for 50 and 90 percent of total vehicle emissions, respectively.

In 2017, Beijing launched new solutions to control vehicle emissions, according to Ai Yi, deputy director of vehicle emission management department of the Beijing Municipal Environmental Protection Bureau.

The solutions included phasing out of older vehicles, limiting the number of vehicles with high emissions entering Beijing and increasing the frequency of inspections.

Three-way catalytic converters are an emissions control devices used in vehicles that convert toxic pollutants in exhaust gas.

In 2017, about 8,000 taxis using more than two-year-old three-way catalytic converters were required to fi t new ones under the city's environmental protection framework.

More than 496,000 older vehicles were phased out, surpassing the annual goal of 300,000.

Since Sept 21, heavy-duty diesel vehicles that failed to meet the National III emission standards were forbidden to enter Beijing's sixth ring road.

Ai said that in order to control motor vehicle emissions, Beijing is striving to improve vehicle standards and oil quality, get older vehicles off the road and enhance inspections on vehicle emissions.

The inspection of vehicle emissions will take place throughout the whole process of vehicle production and before they are put into the market, to fully ensure emission standards, Ai added.

As of Jan 1, the quality of petrol and diesel supplied at the pump vastly improved with the city implementing a six-stage quality system in line with the most stringent international standards.

The quality of fuel now complies with major environmental protection indexes such as gasoline olefins, aromatics, benzene, vapor pressure, distillation and polyaromatic hydrocarbons.

In 2013, the Chinese government issued an action plan for air pollution control, which announced that the annual average concentration of PM2.5 in Beijing should be controlled at around 60 micrograms per cubic meter by 2017.

According to Yu Jianhua, chief engineer of the Beijing Municipal Environmental Protection Bureau, the city used to decrease the number of cars on streets according to their license plate number, but that is not the only measure.

"In the future, the environmental protection department will roll out more measures to control vehicle emissions and perform more detailed analysis of the source of air pollution to create a scientific solution," Yu said.